This letter fold is really very easy. The only tricky bit is pushing the last flap under the adjacent one.
It should be reasonably clear how to fold this from the crease pattern but here are some hints.
Divide the paper into four equal columns in both directions.
During the cupboard folds you will use to get the outer creases fold over the corners as indicated. Unless you are using very thin paper it helps the collapse process if you don't fold the corners quite to their marker creases. Leave a slight gap so that the paper does not buckle when you fold the sides in during the final collapse.
Open the whole thing up and start collapsing by refolding in a clockwise direction.
With this crease pattern in this orientation start collapsing by folding over the right hand column. Then refold the corner crease. Next fold over the bottom panel. Then fold over the corner crease. Fold over the left hand column and then refold its corner. Folding the upper panel over is a little tricky because it has to go under the right hand column and a mountain crease has to be flattened. The final fold is tucking under the last corner.
